package com.anlu.thread.ta4;

import java.util.concurrent.TimeUnit;
import java.util.concurrent.locks.AbstractQueuedSynchronizer;
import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.Lock;

/**
 * @description:
 * @author: Andrew
 * @create: 2019-01-30 15:40
 **/
public class Mylock2 implements Lock{
    private Helper helper = new Helper();

    private class Helper extends AbstractQueuedSynchronizer{
        @Override
        protected boolean tryAcquire(int arg) {
            //如果第一个线程进来，可以拿到锁，因此我们可以返回true，
            //如果第二个线程进来，则拿不到锁，返回false,有种特例，如果当前进来的线程和当前保存的线程是同一个线程，
            //则可以拿到锁，但是有代价，要更新状态值
            //如何判断是第一个线程进来还是其他线程进来？
            int state=getState();
            Thread t = Thread.currentThread();
            if(state==0){
                if(compareAndSetState(0,arg)){
                    setExclusiveOwnerThread(t);
                    return true;
                }
            }else if(getExclusiveOwnerThread()==t){
                setState(state + 1);
                return true;
            }

            return false;
        }

        @Override
        protected boolean tryRelease(int arg) {
            // 锁的获取和释放肯定是一一对应的，那么调用此方法的线程一定是当前线程
            if(Thread.currentThread()!=getExclusiveOwnerThread()){
                throw  new RuntimeException();
            }

            int state = getState() - arg;
            boolean flag=false;
            if(state==0){
                setExclusiveOwnerThread(null);
                flag=true;
            }
            setState(state);
            return flag;

        }
        Condition newCondition() {
            return new ConditionObject();
        }
    }

    @Override
    public void lock() {
        helper.acquire(1);
    }

    @Override
    public void lockInterruptibly() throws InterruptedException {
        helper.acquireInterruptibly(1);
    }

    @Override
    public boolean tryLock() {
        return helper.tryAcquire(1);
    }

    @Override
    public boolean tryLock(long time, TimeUnit unit) throws InterruptedException {
        return helper.tryAcquireNanos(1, unit.toNanos(time));
    }

    @Override
    public void unlock() {
            helper.release(1);
    }

    @Override
    public Condition newCondition() {
                return helper.newCondition();
    }
}
